Method and apparatus for efficient paging and registration in a wireless communications network

ABSTRACT

Method and apparatus for optimizing registration and paging in a group communication system use mobility of the mobile stations to minimize the frequency of registrations performed by the mobile stations as well as the area of paging the mobile stations. When the mobile stations have a low mobility status, the base station reduces the area of paging the mobile stations so that the paging channel load is reduced.

FIELD

[0001] The present invention relates to point to multi-pointcommunications systems. More specifically, the present invention relatesto methods and apparatus for optimizing the frequency of registrationsas well as the area of paging in a wireless group communication network.

BACKGROUND

[0002] In wireless communications systems, registration is the processby which the mobile station notifies the base station of its location,status, identification, slot cycle, and other characteristics. Themobile station informs the base station of its location and status sothat the base station can efficiently page the mobile station whenestablishing a mobile station-terminated call. On the other hand, paginga mobile station includes the act of seeking the mobile station when acall is to be placed to that mobile station. To conserve systemcapacity, reduce service cost, and save battery life, it is desirable tominimize registration as well as paging channel load. However, the actof minimizing registration may be accompanied by a considerable increasein the paging area, and hence an increase in the paging channel load.Current registration and paging techniques are not optimized based onthe mobility of the mobile stations.

[0003] For example, a class of wireless services intended for quick,efficient, one-to-one or one-to-many (group) communication has existedin various forms for many years. In general, these services have beenhalf-duplex, where a user presses a “push-to-talk” (PTT) button on aphone/radio to initiate a group call. If granted the floor, the talkerthen generally speaks for a few seconds. After the talker releases thePTT button, other users may request the floor. These services havetraditionally been used in applications where one person, a“dispatcher,” needs to communicate with a group of people, such as fieldservice personnel or taxi drivers, which is where the “dispatch” namefor the service comes from. Similar services have been offered on theInternet and are generally known as “voice chat.” A key feature of theseservices is that mobile stations participating in a group call generallytend to be of low mobility. Therefore, registration and paging may beoptimized accordingly.

[0004] There is a need, therefore, for mechanisms to minimizeregistration without having to page in a wider area. There is also aneed to optimize registration and paging of a group of mobile stationsbased on the mobility of the mobile stations.

SUMMARY

[0005] The disclosed embodiments provide novel and improved methods andapparatus for optimizing registration and paging of mobile stations in awireless communication network. In one aspect, a method in a mobilestation (MS) for registering the MS with a base station (BS) includesthe steps of determining the number of cells identified in a first listand registering the MS with the BS, if the number of cells identified inthe first list is equal to a predetermined limit.

[0006] In one aspect, a method for paging a target mobile station (MS)includes the steps of receiving information destined for a target MS andpaging the target MS at a paging area that is centered at a cell, inwhich the target MS last registered, and expands by a predefined numberof cells around the cell.

[0007] In another aspect, an apparatus for paging a target mobilestation (MS) includes a memory unit, a receiver, a transmitter, and aprocessor communicatively coupled with the memory unit, the receiver,and the transmitter. The processor is capable of executing instructionsto carry out the above-mentioned methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features and advantages of the present invention will becomemore apparent from the detailed description of the embodiments inconnection with the drawings set forth below:

[0009]FIG. 1 illustrates a group communications system;

[0010]FIG. 2 illustrates an embodiment for a base station and a mobilestation operating in FIG. 1;

[0011]FIG. 3 illustrates how several mobile stations interact with agroup call server;

[0012]FIG. 4 illustrates an embodiment for a group call server in FIG.1;

[0013]FIG. 5 illustrates a call-setup process;

[0014]FIG. 6 illustrates call-signaling details for a network-initiatedinformation delivery process;

[0015]FIG. 7 illustrates a process for buffering location informationfor mobile stations;

[0016]FIG. 8 illustrates a configuration for a group communicationnetwork;

[0017]FIG. 9 illustrates an alternative configuration for a groupcommunication network;

[0018]FIG. 10 illustrates a network-initiated information deliveryprocess;

[0019]FIG. 11 illustrates a registration process;

[0020]FIG. 12 illustrates a cell layout; and

[0021]FIG. 13 illustrates a paging process.

DETAILED DESCRIPTION

[0022] Before several embodiments are explained in detail, it is to beunderstood that the scope of the invention should not be limited to thedetails of the construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Also,it is to be understood that the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting.

[0023]FIG. 1 illustrates a functional block diagram of a groupcommunication system 100, for implementing one embodiment. Groupcommunication system 100 is also known as a push-to-talk (PTT) system, anet broadcast service (NBS), a dispatch system, or apoint-to-multi-point communication system. In one embodiment, groupcommunication system 100 includes a group call server 102, which may bedeployed in either a centralized deployment or a regionalizeddeployment.

[0024] Group mobile stations (MSs) 104 and 106, which may be deployedsuch as cdma2000 handset, for example, may request packet data sessionsusing a data service option. Each MS may use the session to register itsInternet Protocol (IP) address with the group call server 102 to performgroup call initiations. In one embodiment, group call server 102 isconnected to the service provider's packet data service nodes (PDSNs)114 through service provider's network 116. Mobile stations 104 and 106,upon requesting packet data sessions from the wireless infrastructure,may have IP connectivity to group call server 102 through the PDSNs 114.Each PDSN may interface to a base station controller (BSC) through apacket control function (PCF) 108 and a network 112. The PCF may beco-located with the BSC within a base station (BS) 110. A number of BSCsmay be connected to a mobile station controller (MSC) 118.

[0025] A packet data service node may fall in one of several states,e.g., active or connected state, dormant state, and null or inactivestate. In the active or connected state, an active traffic channelexists between the participating MS and the BS or BSC, and either sidemay send data. In the dormant state, no active traffic channel existsbetween the participating MS and the BSC, but a point-to-point protocol(PPP) link is maintained between the participating MS and the PDSN. Inthe null or inactive state, there is no active traffic channel betweenthe participating MS and the BSC, and no PPP link is maintained betweenthe participating MS and the PDSN.

[0026] After powering up, mobile stations 104 and 106 may request packetdata sessions. As part of establishing a packet data session, each MSmay be assigned an IP address. Each MS may perform a registrationprocess to notify group call server 102 of the MS's IP address.Registration may be performed using an IP protocol, such as sessioninitiation protocol (SIP) over user datagram protocol (UDP). The IPaddress of a MS may be used to contact the MS when the correspondinguser is invited into a group call.

[0027] Once a group call is established, mobile stations 104 and 106 andgroup call server 102 may exchange media and signaling messages. In oneembodiment, media may be exchanged between the participating mobilestations and the group call server by using real-time protocol (RTP)over UDP. The signaling messages may also be exchanged by using asignaling protocol over UDP.

[0028] Group communication system 100 performs several differentfunctions in order to provide group call services. The functions thatrelate to the user side include user registration, group callinitiation, group call termination, sending alerts to groupparticipants, late join to a group call, talker arbitration, addingmembers to a group, removing members from a group, un-registering amember, and user and/or device authentication. The functions that relateto system preparation and operation include administration andprovisioning, scalability, and reliability. These functions aredescribed in detail in the copending patent application, U.S. patentapplication Ser. No. 10/076,726, filed Feb. 14, 2002, which is assignedto the same assignee and incorporated herein by reference in itsentirety.

[0029]FIG. 2 is a simplified block diagram of an embodiment of basestation 204 and mobile station 206, which are capable of implementingvarious disclosed embodiments. For a particular communication, voicedata, packet data, and/or messages may be exchanged between base station204 and mobile station 206, via an air interface 208. Various types ofmessages may be transmitted, such as messages used to establish acommunication session between the base station and mobile station,registration and paging messages, and messages used to control a datatransmission (e.g., power control, data rate information,acknowledgment, and so on). Some of these message types are described infurther detail below.

[0030] For the reverse link, at mobile station 206, voice and/or packetdata (e.g., from a data source 210) and messages (e.g., from acontroller 230) are provided to a transmit (TX) data processor 212,which formats and encodes the data and messages with one or more codingschemes to generate coded data. Each coding scheme may include anycombination of cyclic redundancy check (CRC), convolutional, turbo,block, and other coding, or no coding at all. The voice data, packetdata, and messages may be coded using different schemes, and differenttypes of messages may be coded differently.

[0031] The coded data is then provided to a modulator (MOD) 214 andfurther processed (e.g., covered, spread with short PN sequences, andscrambled with a long PN sequence assigned to the user terminal). Themodulated data is then provided to a transmitter unit (TMTR) 216 andconditioned (e.g., converted to one or more analog signals, amplified,filtered, and quadrature modulated) to generate a reverse link signal.The reverse link signal is routed through a duplexer (D) 218 andtransmitted via an antenna 220 to base station 204.

[0032] At base station 204, the reverse link signal is received by anantenna 250, routed through a duplexer 252, and provided to a receiverunit (RCVR) 254. Base station 204 may receive registration informationand status information, e.g., mobile station mobility rate, from mobilestation 206. Receiver unit 254 conditions (e.g., filters, amplifies,down converts, and digitizes) the received signal and provides samples.A demodulator (DEMOD) 256 receives and processes (e.g., despreads,decovers, and pilot demodulates) the samples to provide recoveredsymbols. Demodulator 256 may implement a rake receiver that processesmultiple instances of the received signal and generates combinedsymbols. A receive (RX) data processor 258 then decodes the symbols torecover the data and messages transmitted on the reverse link. Therecovered voice/packet data is provided to a data sink 260 and therecovered messages may be provided to a controller 270. Controller 270may include instructions for determining a paging area, paging a groupof mobile stations, and sending information to the mobile stations. Theprocessing by demodulator 256 and RX data processor 258 arecomplementary to that performed at mobile station 206. Demodulator 256and RX data processor 258 may further be operated to process multipletransmissions received via multiple channels, e.g., a reversefundamental channel (R-FCH) and a reverse supplemental channel (R-SCH).Also, transmissions may be simultaneously from multiple mobile stations,each of which may be transmitting on a reverse fundamental channel, areverse supplemental channel, or both.

[0033] On the forward link, at base station 204, voice and/or packetdata (e.g., from a data source 262) and messages (e.g., from controller270) are processed (e.g., formatted and encoded) by a transmit (TX) dataprocessor 264, further processed (e.g., covered and spread) by amodulator (MOD) 266, and conditioned (e.g., converted to analog signals,amplified, filtered, and quadrature modulated) by a transmitter unit(TMTR) 268 to generate a forward link signal. The forward link signal isrouted through duplexer 252 and transmitted via antenna 250 to mobilestation 206. Forward link signals include paging signals.

[0034] At mobile station 206, the forward link signal is received byantenna 220, routed through duplexer 218, and provided to a receiverunit 222. Receiver unit 222 conditions (e.g., down converts, filters,amplifies, quadrature modulates, and digitizes) the received signal andprovides samples. The samples are processed (e.g., despreaded,decovered, and pilot demodulated) by a demodulator 224 to providesymbols, and the symbols are further processed (e.g., decoded andchecked) by a receive data processor 226 to recover the data andmessages transmitted on the forward link. The recovered data is providedto a data sink 228, and the recovered messages may be provided tocontroller 230. Controller 230 may include instructions for determiningthe number of pilot signals in an active set, adding new pilots in theactive set, moving pilot signals from a list to another list,registering mobile station 206, and providing the registrationinformation to the base station 204.

[0035] The group call service (GCS) may allow one user to talk to agroup of users in a half-duplex or full-duplex mode. In the former case,because only one person may be permitted to talk at a time, thepermission to talk may be moderated by the infrastructure. In suchsystems, a user may request permission to talk by pressing a“push-to-talk” button (PTT), for example. The system may arbitrate therequests received from multiple users and, through acontention-resolution process, the system may choose one of therequestors according to a predetermined algorithm. The system may thennotify the chosen user that the user has permission to talk. The systemmay transparently dispatch the user's traffic information, such as voiceand/or data, from the authorized talker to the rest of the groupmembers, who may be considered “listeners.” The voice and/or datatraffic in GCS may be different from the classical one-to-one phonecall, and a priority may be placed on some conversations.

[0036]FIG. 3 illustrates a group call arrangement for showing how mobilestations (MSs) 302, 304, and 306 interact with a group call server 308.Multiple group call servers may be deployed as desired for large-scalegroups. In FIG. 3, when MS 302 has permission to transmit media to othermembers of the group, MS 302 is known as the talker and may transmitmedia over an established channel. When MS 302 is designated as thetalker, the remaining participants, MS 304 and MS 306, may not havepermission to transmit media to the group. Accordingly, MS 304 and MS306 are designated as listeners. As described above, MSs 302, 304, and306 are connected to group call server 308, using at least one channel.In one embodiment, channels 310, 312, and 314 may include a sessioninitiation protocol (SIP) channel, a media-signaling channel, and amedia traffic channel.

[0037]FIG. 4 illustrates one embodiment for the group call server 102operating in the system of FIG. 1. The group call server includesantennas 402, 404 for transmitting and receiving data. Antenna 402 iscoupled to the receiver circuitry 406 and antenna 404 is coupled to thetransmit circuitry 408. Communication bus 410 provides a commonconnection among other modules in FIG. 4. Communication bus 410 isfurther coupled to memory unit 412. Memory 412 stores computer readableinstructions for a variety of operations and functions performed by thegroup call server. The processor 414 performs the instructions stored inmemory 412.

[0038]FIG. 5 illustrates a message-flow diagram showing a group callsetup, according to one embodiment. A user who wishes to initiate agroup call selects one or more target users, one or more pre-definedgroups, or a combination of the two and may depress the push-to-talk(PTT) button on a MS. The caller's MS may be in a dormant packet datasession when the caller initiates the group call. The caller's MS thensends a group call request 502 to the group call server to setup thegroup call. The group call request may be transmitted regardless ofwhether the caller's MS has a dedicated traffic channel or not. Afterthe group call request is sent, if the caller's MS is in dormant packetdata session, the caller's MS initiates the process of re-establishingits dedicated traffic channel and prepare the packet data session formedia activity.

[0039] When the group call server receives the group call request, thegroup call server expands the pre-defined groups, if any is specified inthe received group call request, into a list of group members. The groupcall server retrieves location information for the desired groupmembers. The group call server also determines if the target group isalready running in the system.

[0040] After the group call server locates at least one of the groupmembers, the group call server sends an announcement 504 back to thecaller's MS indicating that the group call is being set up. At thispoint, the caller's MS optimistically grants the caller's request totalk. The caller's MS starts buffering the received media for futuretransmission to the group call server. The group call server uses thelocation information of the target listeners' mobile stations to sendout announcements 506 to the target listeners' Mobile stations. Sendingthe announcements triggers the packet data sessions of the targetlisteners' mobile stations to come out of dormancy and to re-establishtheir traffic channels.

[0041] The “instant response” relates to the response time it takes forthe group call server to respond to a PTT or group call request. Thegoal for responding to the PTT or group call request is to consistentlyrespond to the request within a predetermined time period, e.g., onesecond or less. In many cases, when a caller requests to setup a groupcall, the caller's packet data session is dormant, meaning that nodedicated traffic channel exists. Re-establishing dedicated trafficchannels may take considerable time.

[0042] In one embodiment, group communication system 100 (FIG. 1)supports both chat-room and ad-hoc models for group call services. Inthe chat-room model, groups are predefined, which may be stored on thegroup call server. The predefined groups, or nets, may be public,implying that the group has an open member list. In this case, eachgroup member is a potential participant in a group call. The group callis started when a first group member starts to initiate a group call.The call remains running for a pre-determined time period, which may beconfigured by the service provider. During a group call, the groupmembers may specifically request to join or leave the call. Duringperiods of talk inactivity, the group call may be brought into a groupdormant state until a group member requests permission to talk. Whenoperating in the chat-room model, group members, also known as netmembers, communicate with one another using a mobile station assigned toeach net member. The term “net” denotes a group of members authorized tocommunicate with each other.

[0043] In the ad-hoc model of group call services, however, groups maybe defined in real-time and have a closed member list associated witheach group. A closed member list may specify which members are allowedto participate in the group call. The member list may not be availableto others outside of the closed member list, and may only exist for thelife of the call. Ad-hoc group definitions may not be stored in thegroup call server. The definitions may be used to establish the groupcall and released after the call has ended. An ad-hoc group may beformed when a caller selects one or more target members and generates agroup call request, which is sent to the group call server to start thecall. The group call server may send a notification to the target groupmembers that they have been included in the group. The group call servermay automatically join the target members into the group call, i.e., noaction may be required from the target members. When an ad-hoc callbecomes inactive, the group communication server may “tear down” thecall and free the resources assigned to the group, including the groupdefinition used to start the call.

[0044] Network-Originated Call-Signaling Messages

[0045] In one embodiment, after receiving the floor-control request, thegroup call server may burst media-signaling messages to a group ofdormant target Mobile stations and trigger the dormant target Mobilestations to re-establish their dedicated traffic channels. In oneembodiment, the packet control function (PCF) receives a small amount ofinformation, e.g., packet data, from the packet data serving node(PDSN), which may be destined for a dormant target MS. The PCF maychoose to send the information to the base station controller (BSC) in aspecial form. In one embodiment, the special form includes short databurst (SDB) format, as specified in the TIA/EIA/IS-707-A-2, “DataService Option Standard for Spread Spectrum

[0046] Systems,” Addendum 2, dated June 2000 (IS-707-A-2). TheTLI/ELI/IS-2001-A, “Interoperability Specification (IOS) for cdma2000Access Network Interfaces,” dated August 2001 (IS-2001-A) standarddefines several options for the BSC to deliver SDB messages to targetMobile stations.

[0047] According to the IS-2001-A standard, for example, when a smallamount of data destined for a dormant target MS is received at the PCF,the PCF may choose to send the received data to the BSC in SDB format.If the BSC determines that short data bursts may be used to deliver thedata to the dormant target MS, the BSC may send the data directly to thedormant target MS over a signaling channel. The BSC may also send thedata to the MSC for delivery to the dormant target MS via an applicationdata delivery service (ADDS) Page. The data may be delivered to the MSCusing a BSC service request/response procedure. If the BSC isunsuccessful in delivering the SDB data to the dormant target MS on itsown, the BSC may choose to send the data to the MSC for delivery to thedormant target MS via the ADDS Page procedure.

[0048]FIG. 6 shows a call-flow procedure for delivering data to a targetMS, according to one embodiment. The packet data session is in thedormant state 602 with PPP connected. The PDSN sends packet data 604 tothe PCF on the existing PPP connection associated with the target MS.The PCF sends the packet data 606 to the BSC. The PCF also buffers thepacket data. The BSC acknowledges receiving the data packets from thePCF by returning an acknowledge message 608, which includes anindication that the BSC attempts to send the data to the target MS. ThePCF then discards the data that it had buffered.

[0049] The BSC sends the packet data directly to the target MS or,alternatively, the BSC uses an ADDS Page procedure to deliver the packetdata, e.g., in SDB form, to the target MS. If the BSC directly sends thepacket data 610 to the target MS, the target MS sends an acknowledgement612 in response to receiving the data. If an acknowledgement is notreceived from the target MS, the BSC may choose not to send the packetdata or may request the MSC to deliver the packet data via ADDS Pageprocedure.

[0050] If the BSC could not successfully send the packet data 610 to thetarget MS, the BSC sends a “BSC service request” 614, which contains thepacket data, to the MSC. The MSC acknowledges receiving the BSC servicerequest message by sending a “BSC service response” 616 to the BSC. TheMSC then sends an ADDS Page message 618 to the BSC for delivering thepacket data to the target MS. If the MSC sends the packet data, the MSCspecifies the “data type field” in the ADDS Page to “SDB.” The ADDS Pagemessage contains the location information for the target MS.Accordingly, the BSC forwards the data 620, e.g., in SDB form, to thetarget MS. The target MS sends an acknowledgement message 622 afterreceiving the data from the BSC. If the MSC had requested in the ADDSPage message, the BSC returns an ADDS Page acknowledgement message 624to the MSC, after receiving the acknowledgement message from the targetMS. The BSC also sends an update message 626 to the PCF to indicatesuccessful transmission of the data to the target MS. The PCF responds628 to the BSC with an update acknowledge message. The PCF sends aregistration request 630 to the PDSN, which responds with a registrationreply message 632.

[0051] Having the BSC directly deliver the packet data to the target MSmay minimize the delay, but the target MS may not receive the databecause the target MS may have moved out of the BSC's paging area by thetime the data arrive. Since the MSC maintains location information forthe target MS, the ADDS Page data delivery process ensures that thetarget MS receives the data. In one embodiment, the BSC may cachelocation information for the target MS, which may be used by the BSCwhen there is data destined for the target MS. Using the locationinformation cached at the BSC eliminates the delay due to having the BSCto request the MSC to send the ADDS Page. This process provides assureddelivery of the data to the target MS based on the saved locationinformation.

[0052] On embodiment of cashing location information for the mobilestations is illustrated in FIG. 7. The BSC caches 702, 704 the targetMS's location information after the BSC receives a page response 706from the target MS or receives a “location update accept” message 708from the MSC. The page response message received from the target MS mayinclude a cell identifier field that specifies the location, e.g., acell location area code (LAC), of the target MS. In one embodiment, theBSC may obtain the target MS's location information from the target MS'sregistration message. For example, there are several different types ofregistration defined by the TIA/ELA/IS-2000.5-A, “Upper Layer (Layer 3)Signaling Standard for cdma2000 Spread Spectrum Systems,” dated November2000 (IS-2000 standard). Any of these registration types may provide theBSC information about the location of the target MS. The BSC may updatethe cached location information if the BSC receives a page response, aregistration response, an origination message, or other signalingmessages that provide the current location information for the targetMS.

[0053] Network Configurations

[0054] Each PCF in the network may be uniquely identified by a systemidentification/network identification/packet zone identification(SID/NID/PZID) code. When the target MS moves from one PCF to anotherPCF, i.e., PCF to PCF handoff, during the dormant packet data session,the target MS may be required to re-register to have the PDSN establishan interface with the new PCF and terminate the existing connection withthe old PCF.

[0055] In one embodiment, as shown in FIG. 8, the BSC and the PCF areco-located. When a packet data arrives at the PCF and the PCF decides tosend the packet data, the target MS may most probably be under theservice area of the same BSC. Otherwise, the target MS would have beenrequired to re-register and a new connection would have been establishedwith a different PCF.

[0056] In one embodiment, as shown in FIG. 9, the BSC and the PCF arenot co-located. In FIG. 9, BSC₁ is shown to be fully interconnected withother BSCs that are connected to the same PCF. The BSCs that areconnected to the same PCF may be interconnected either viapoint-to-point link or via a switching network. Unlike the scenariowhere the BSC and the PCF are co-located, when the PCF sends data toBSC₁, BSC₁ may fail in delivering the data to the target MS because thetarget MS may have moved outside the service area of BSC₁ to anotherBSC's service area. In FIG. 9, for example, the target MS may have beenin the service area of BSC₁ before the packet data session goes dormant,and may have moved to the service area of BSC₅ when BSC₁ receives therequest from the PCF to deliver data to the target MS.

[0057] In one embodiment, where the PCF may be co-located with the BSC,the BSC receives the packet data for transmission to a target MS, whichmay be dormant. The BSC may broadcast the packet data to the cellsand/or sectors within the BSC's service area. Alternatively, to decreaseair-link resource consumption, the BSC may utilize the target MS'slocation information, which may have been already cached at the BSC, tobroadcast the data to a subset of cells and/or sectors under the BSC'scontrol.

[0058] In one embodiment, where the PCF may be co-located with the BSC,as shown in FIG. 10, the BSC receives the packet data 1002 from the PDSNfor delivery to a target MS. Before the BSC sends the packet data 1002to the target MS, the BSC first buffers the packet data. The BSC thendetermines 1004 a paging zone for paging the target MS, as will bedescribed in more detail herein later. The BSC then sends out a pagemessage 1006 based on the determined paging zone under the BSC's servicearea. If the target MS's identification information, such as thematching mobile identification number (MIN) or electronic serial number(ESN), matches with the identification information specified in thepaging message, the MS sends a paging response 1008 to the BSC. Thepaging response provides information about the cell and/or sector thetarget MS is located in, which allows the BSC to send the packet data tothe identified cell and/or sector only. The BSC caches 1010 the targetMS's location information before sending the packet data 1012 to thetarget MS. The cached location information may be refreshed by the nextpage response, registration response, origination message, or othersignaling messages that provide location information for the target MS.The cached location information may be aged out by a timer.

[0059] Cell-Based Registration Scheme

[0060] Registration is the process by which the MS notifies the basestation of its location, status, identification, slot cycle, and othercharacteristics. The MS informs the base station of its location andstatus so that the base station can efficiently page the MS whenestablishing a MS-terminated call. While the MS is in idle state, the MSmay perform registration when an idle handoff occurs. An idle handoffoccurs when a MS has moved from the coverage area of one base stationinto the coverage area of another base station during the MS idle state.If the MS detects a pilot channel signal from another base station thatis sufficiently stronger than that of the current base station, the MSdetermines that an idle handoff should occur.

[0061] Idle handoff is the act of transferring reception of the pagingchannel, broadcast control channel or the forward common control channelfrom one base station to another base station, when the MS is in theidle state. The MS in an idle state determines that an idle handoff isneeded if the pilot signal strength of the new cell is certain decibelsgreater than the pilot signal in its Active Set.

[0062] When the MS transits from other states to the idle state, the MSmay initialize two lists of cells. The first list is namedCURRENT_CELL_LIST and the second list is named PREV_CELL_LIST. As the MSperforms an idle handoff, the mobile station adds the new cell'sidentification information into the CURRENT_CELL_LIST if the new cell isnot already identified in the list. The MS may obtain the new cell'sinformation by listening to the broadcasted overhead messages.

[0063] In one embodiment, if the number of cells in theCURRENT_CELL_LIST list reaches a predetermined limit, e.g.,MAX_NUM_CELLS, the MS performs a registration and copies the entries inthe CURRENT_CELL_LIST, except the last entry, into the PREV_CELL_LIST.Thus, the size of the PREV_CELL_LIST is equal to the predeterminedlimit, e.g., MAX_NUM_CELLS, less one.

[0064]FIG. 11 illustrates a registration process, according to oneembodiment. The CURRENT_CELL_LIST includes at least the identificationinformation of the cell in which the MS last registered, 1102. As the MSdetects a new pilot signal that may be added to the active set, the MSadds the identification information of the new cell in theCURRENT_CELL_LIST, in step 1104, if the cell is not already identifiedin the CURRENT_CELL_LIST. In step 1106, the MS determines whether thenumber of cells identified in the CURRENT_CELL_LIST has reached thepredetermined limit, e.g., MAX_NUM_CELLS. If the number of cells in theCURRENT_CELL_LIST has reached the predetermined limit, the MS performs aregistration, in step 1108, and moves the identification information ofthe cells in the CURRENT_CELL_LIST, except the last entered cell inwhich the MS registered, to the PREV_CELL_LIST, in step 1110.

[0065] In one embodiment, the cell layout is shown as in FIG. 12.Letting the predetermined limit, MAX_NUM_CELLS, to be three and the MS'strajectory from cell to cell to be A1→B2→C3, and assuming the cell inwhich the mobile last registered is A1, 1202, the CURRENT_CELL_LISTwould contain cell {A1}. After the MS detects the pilot signal of cellB2, 1204, and adds cell B2 to the CURRENT_CELL_LIST, the latter containscells {A1, B2}. As the MS moves toward cell C3, 1206, the MS detects andadds cell C3 to the CURRENT_CELL_LIST, which now contains cells {A1, B2,C3}. Now, since the number of cells identified in the CURRENT_CELL_LISTequals the predetermined limit, e.g., three, the MS performs aregistration with the network and moves the cells {A1, B2} from theCURRENT_CELL_LIST to the PREVIOUS_CELL_LIST.

[0066] Paging a mobile station includes the act of seeking the mobilestation when a call is to be placed to that mobile station. To conservesystem capacity, reduce service cost, and save battery life, it isdesirable to minimize paging area to reduce the paging channel load. Thepaging area may be configured, e.g., predefined or dynamicallydetermined, for a given BSC. The paging area may be different fordifferent BSCs. The BSC pages the target MS in the configured pagingarea. If the target MS cannot be located in the configured paging areaof the BSC, the data may be sent to a neighboring BSC for delivering tothe target MS. Therefore, each BSC need not to unnecessarily page in alarge area. If the target MS cannot be located in the paging area of theBSCs connected to a mobile station controller (MSC), the data may besent to the MSC for delivering to the target MS, if the MSC could locatethe target MS.

[0067]FIG. 13 shows a paging scheme, according to one embodiment. Instep 1302, the BSC receives registration information from the target MS,which is located in the cell X. When the BSC receives information, e.g.,data, voice, image, text, video, or any combination thereof, fordelivery to the target MS, in step 1304, the BSC pages the target MSbased on a paging area, which may be a predefined area or a dynamicallydetermined area. In step 1306, the BSC configures the paging area basedon a certain number of cells from or around the cell in which the targetMS last registered. For example, the paging area may include the cellsthat fall within an area that is centered at cell X and extended by apredetermined number of cells, e.g., MAX_NUM_CELLS less one.

[0068] After the BSC pages the target MS based on the configured pagingarea, the BSC waits for a paging response from the target MS, in step1308. If the BSC could locate the target MS from the paging response,the BSC sends the information destined for the target MS to the targetMS, in step 1310. However, if the BSC could not locate the target MSfrom the paging response, the BSC requests a neighboring BSC to locatethe target MS, which may be by the same paging scheme discussed above.If the neighboring BSC locates the target MS, in step 1312, the BSCsends the information destined for the target MS to the neighboring BSCfor delivery to the target MS, in step 1314.

[0069] If none of the BSCs connected to the MSC could locate the targetMS, the MSC is requested to locate the target MS, which may be based ona flood paging scheme. If the MSC locates the target MS, in step 1316,the BSC holding the information destined for the target sends theinformation to the MSC to for delivery to the target MS, in step 1318.In case the MSC could not locate the target MS, the MS may not be founddue to being turned off or being out of service 1320.

[0070] For example, letting the trajectory of the target MS from cell tocell to be “A→B→C→D→E→D→C→B→F,” the predetermined limit, e.g.,MAX_NUM_CELLS, to be three, and assuming the cell in which the MS lastregistered is cell A, the CURRENT_CELL_LIST would contain cell {A}.After the MS detects and adds cell B to the CURRENT_CELL_LIST, thelatter contains cells {A, B}. As the MS moves toward cell C, the MSdetects and adds cell C to the CURRENT_CELL_LIST, making it to containnow cells {A, B, C}. Since the number of cells in the CURRENT_CELL_LISTequals to the predetermined limit, e.g., 3, the MS performs aregistration in cell C and moves cells {A, B} from the CURRENT_CELL_LISTto the PREVIOUS_CELL_LIST.

[0071] As the MS moves through cell D, and then to cell E, the MS addscells D and E to the CURRENT_CELL_LIST, making it to contain now cells{C, D, E}. Since the number of cells in the CURRENT_CELL_LIST equals thepredetermined limit, e.g., three, the MS performs a registration in cellE and moves cells {C, D} from the CURRENT_CELL_LIST to thePREVIOUS_CELL_LIST.

[0072] As the MS moves back to cell D, and then to C, the MS does notadd cells D and C to the CURRENT_CELL_LIST, because these cells arealready included in current PREVIOUS_CELL_LIST. However, when the MSmoves back to cell B, the MS adds the identification information of thecell B to the CURRENT_CELL_LIST, because cell B is not included in thePREVIOUS_CELL_LIST, which now includes cells C and D.

[0073] As the MS moves through a new cell F, the MS detects and addscell F to the CURRENT_CELL_LIST, which now contains cells {E, B, F}.Since the number of cells in the CURRENT_CELL_LIST equals thepredetermined limit of three, e.g., MAX_NUM_CELLS, the MS performs aregistration in cell F and moves cells {E, B} from the CURRENT_CELL_LISTto the PREVIOUS_CELL_LIST.

[0074] In one embodiment, where the PCF may not be co-located with theBSC, the BSC receives a request from the PCF to send the packet data tothe target MS. The BSC determines if the BSC has cached locationinformation for the target MS. If the BSC had cached locationinformation for the target MS, which allows the BSC to perform assureddata delivery, the BSC sends the data to the target MS, according to thecached location information. Otherwise, if the BSC did not have locationinformation for the target MS, the BSC may send a page message to apredetermined paging zone to locate the target MS. If BSC could locatethe target MS, the BSC then sends the data received from the PCF to thetarget MS. However, if the BSC could not locate the target MS in thepredetermined paging zone, the BSC may send the data to a neighboringBSC, which may be connected to the same MSC, so that one of theneighboring BSCs that has location information for the target MS, or canlocate the target MS, transmits the information to the target MS. TheBSC that has cached location information for the target MS, or canlocate the target MS, delivers the data to the target MS. If no BSC haslocation information for the target MS, nor can locate the target MS,the data may be sent to the MSC to be delivered to the target MS, e.g.,via flood paging. The MSC may not locate the target MS, due to thetarget MS being turned off or out of service. Therefore, the disclosedembodiments provide for a significant reduction in the number ofregistrations as well as the paging area, thus saving battery life andpaging channel load.

[0075] Those of skill in the art would understand that information andsignals may be represented using any of a variety of differenttechnologies and protocols. For example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

[0076] Those of skill would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

[0077] The various illustrative logical blocks, modules, and circuitsdescribed in connection with the embodiments disclosed herein may beimplemented or performed with a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general-purpose processor may be a microprocessor,but, in the alternative, the processor may be any conventionalprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

[0078] The steps of a method or algorithm described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, a hard disk, a removabledisk, a MS-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor, such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

[0079] The description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments may be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments, e.g., in an instantmessaging service or any general wireless data communicationapplications, without departing from the spirit or scope of theinvention. Thus, the present invention is not intended to be limited tothe embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

1. A method in a mobile station (MS) for registering the MS with a basestation (BS), the method comprising: determining a number of cellsidentified in a first list; and registering the MS with the BS if thenumber of cells identified in the first list is equal to a predeterminedlimit.
 2. The method of claim 1, further including moving the cellsidentified in the first list, other than a cell in which the MS lastregistered, to a second list, after said registering the MS.
 3. Themethod of claim 2, further including adding a cell, whose pilot signal'sstrength is higher than or equal to a predetermined threshold, to thefirst list if the cell is not already included in the second list.
 4. Anapparatus for registering a mobile station (MS) with a base station(BS), comprising: means for determining a number of cells identified ina first list; and means for registering the MS with the BS if the numberof cells identified in the first list is equal to a predetermined limit.5. The apparatus of claim 4, further including means for moving thecells identified in the first list, other than a cell in which the MSlast registered, to a second list, after said registering the MS.
 6. Theapparatus of claim 5, further including means for adding a cell, whosepilot signal's strength is higher than or equal to a predeterminedthreshold, to the first list if the cell is not already included in thesecond list.
 7. A computer-readable medium storing codes for enabling aprocessor to perform a method for registering a mobile station (MS) witha base station (BS), the method comprising: determining a number ofcells identified in a first list; and registering the MS with the BS ifthe number of cells identified in the first list is equal to apredetermined limit.
 8. The computer-readable medium of claim 7, themethod further including moving the cells identified in the first list,other than a cell in which the MS last registered, to a second list,after said registering the MS.
 9. The computer-readable medium of claim8, the method further including adding a cell, whose pilot signal'sstrength is higher than or equal to a predetermined threshold, to thefirst list if the cell is not already included in the second list.
 10. Amobile station (MS) comprising: a receiver capable of receivinginformation from a base station (BS); a transmitter capable oftransmitting information to the BS; and a processor capable of carryingout a method for registering the MS with a base station (BS), the methodcomprising: determining a number of cells identified in a first list;and registering the MS with the BS if the number of cells identified inthe first list is equal to a predetermined limit.
 11. The MS of claim10, the method further including moving the cells identified in thefirst list, other than a cell in which the MS last registered, to asecond list, after said registering the MS.
 12. The MS of claim 11, themethod further including adding a cell, whose pilot signal's strength ishigher than or equal to a predetermined threshold, to the first list ifthe cell is not already included in the second list.
 13. A method forpaging a target mobile station (MS), the method comprising: receivinginformation destined for a target MS; and paging the target MS at apaging area that is centered at a cell, in which the target MS lastregistered, and expands by a predefined number of cells around the cell.14. The method of claim 13, further including sending the information tothe target MS, if the target MS is located.
 15. The method of claim 14,further including determining a neighboring base station controller(BSC) that can locate the target MS, if the target MS is not located.16. The method of claim 15, further including sending the information tothe neighboring BSC that locates the target MS for delivery to thetarget MS.
 17. The method of claim 15, further including determiningwhether a mobile station controller (MSC) can locate the target MS, ifno BSC connected to the MSC could locate the target MS.
 18. The methodof claim 17, further including sending the information to the MSC fordelivery to the target MS, if the MSC locates the target MS.
 19. Acomputer-readable medium storing codes for enabling a processor toperform a method for paging a target mobile station (MS), the methodcomprising: receiving information destined for a target MS; and pagingthe target MS at a paging area that is centered at a cell, in which thetarget MS last registered, and expands by a predefined number of cellsaround the cell.
 20. The computer-readable medium of claim 19, themethod further including sending the information to the target MS, ifthe target MS is located.
 21. The computer-readable medium of claim 20,the method further including determining a neighboring base stationcontroller (BSC) that can locate the target MS, if the target MS is notlocated.
 22. The computer-readable medium of claim 21, the methodfurther including sending the information to the neighboring BSC thatlocates the target MS for delivery to the target MS.
 23. Thecomputer-readable medium of claim 21, the method further includingdetermining whether a mobile station controller (MSC) can locate thetarget MS, if no BSC connected to the MSC could locate the target MS.24. The computer-readable medium of claim 23, the method furtherincluding sending the information to the MSC for delivery to the targetMS, if the MSC locates the target MS.
 25. An apparatus for paging atarget mobile station (MS), comprising: means for receiving informationdestined for a target MS; and means for paging the target MS at a pagingarea that is centered at a cell, in which the target MS last registered,and expands by a predefined number of cells around the cell.
 26. Theapparatus of claim 25, further including means for sending theinformation to the target MS, if the target MS is located.
 27. Theapparatus of claim 26, further including means for determining aneighboring base station controller (BSC) that can locate the target MS,if the target MS is not located.
 28. The apparatus of claim 27, furtherincluding means for sending the information to the neighboring BSC thatlocates the target MS for delivery to the target MS.
 29. The apparatusof claim 27, further including means for determining whether a mobilestation controller (MSC) can locate the target MS, if no BSC connectedto the MSC could locate the target MS.
 30. The apparatus of claim 29,further including means for sending the information to the MSC fordelivery to the target MS, if the MSC locates the target MS.
 31. A basestation controller (BSC) for paging a target mobile station (MS),comprising: a receiver capable of receiving information from a targetMS; a transmitter capable of transmitting information to the target MS;and a processor capable of carrying out a method for paging the targetMS, comprising: receiving information destined for a target MS; andpaging the target MS at a paging area that is centered at a cell, inwhich the target MS last registered, and expands by a predefined numberof cells around the cell.
 32. The base station controller of claim 31,the method further including sending the information to the BSC fordelivery to the target MS, if the BSC locates the target MS.
 33. Thebase station controller of claim 32, the method further includingdetermining a neighboring BSC that can locate the target MS, if the BSCcould not locate the target MS.
 34. The base station controller of claim33, the method further including sending the information to theneighboring BSC that locates the target MS for delivery to the targetMS.
 35. The base station controller of claim 33, the method furtherincluding determining whether a mobile station controller (MSC) canlocate the target MS, if no BSC connected to the MSC could locate thetarget MS.
 36. The base station controller of claim 35 the methodfurther including sending the information to the MSC for delivery to thetarget MS, if the MSC locates the target MS.